It is generally known that a semiconductor having few crystal defects and good crystallinity is grown on a substrate by using a substrate lattice-matched with the semiconductor to be grown. There is, however, no substrate that is lattice-matched with a nitride semiconductor, has excellent crystallinity, and allows a nitride semiconductor crystal to be stably grown. For this reason, there is no choice but to grow a nitride semiconductor on a substrate, e.g., a sapphire, spinnel, or silicon carbide substrate, that is not lattice-matched with nitride semiconductors.
Various research institutes have made attempts to manufacture GaN bulk crystals that are lattice-matched with nitride semiconductors. However, it has only been reported that GaN bulk crystals having sizes of several millimeters are obtained. That is, any practical GaN bulk crystal like the one from which many wafers are cut to be actually used as substrates for the growth of nitride semiconductor layers has not been obtained.
As a technique of manufacturing GaN substrates, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 7-202265 and 7-165498 disclose a technique of forming a ZnO buffer layer on a sapphire substrate, growing a nitride semiconductor on the ZnO buffer layer, and dissolving and removing the ZnO buffer layer. However, since the ZnO buffer layer grown on the sapphire substrate has poor crystallinity, it is difficult to obtain a nitride semiconductor crystal having good quality by growing a nitride semiconductor on the buffer layer. In addition, it is difficult to continuously grow a nitride semiconductor thick enough to be used as a substrate on the thin ZnO buffer layer.
When a nitride semiconductor electronic element used for various electronic devices such as a light-emitting diode (LED) device, a laser diode (LD) device, and a light-receiving device is to be manufactured, if a substrate made of a nitride semiconductor having few crystal defects can be manufactured, a new nitride semiconductor having few lattice defects and forming a device structure can be grown on the substrate. Therefore, the obtained device acquires greatly improved performance. That is, a high-performance device that has not been realized in the past can be realized.
It is, therefore, an object of the present invention to provide a method of growing a nitride semiconductor crystal having excellent crystallinity.
More specifically, it is an object of the present invention to provide a method of growing a nitride semiconductor crystal that can provide a nitride semiconductor substrate, a nitride semiconductor substrate, and a nitride semiconductor device formed on the nitride semiconductor substrate.